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Subject: [OMPI devel] RTE Issue II: Interaction between the ROUTED and GRPCOMM frameworks
From: Ralph H Castain (rhc_at_[hidden])
Date: 2007-12-04 10:14:17


II. Interaction between the ROUTED and GRPCOMM frameworks
When we initially developed these two frameworks within the RTE, we
envisioned them to operate totally independently of each other. Thus, the
grpcomm collectives provide algorithms such as a binomial "xcast" that uses
the daemons to scalably send messages across the system.

However, we recently realized that the efficacy of the current grpcomm
algorithms directly hinge on the daemons being fully connected - which we
were recently told may not be the case as other people introduce different
ROUTED components. For example, using the binomial algorithm in grpcomm's
xcast while having a ring topology selected in ROUTED would likely result in
terrible performance.

This raises the following questions:

(a) should the GRPCOMM and ROUTED frameworks be consolidated to ensure that
the group collectives algorithms properly "match" the communication
topology?

(b) should we automatically select the grpcomm/routed pairings based on some
internal logic?

(c) should we leave this "as-is" and the user is responsible for making
intelligent choices (and for detecting when the performance is bad due to
this mismatch)?

(d) other suggestions?

Ralph